To increase the efficiency of refuse collection, many refuse collection companies use automated refuse loaders that lift a refuse container and then dump the refuse container into a refuse collection vehicle. Such automated refuse loaders can service a significantly higher number of customers in a given time period when compared with manually placing refuse into the refuse collection vehicle. This increased efficiency can result in substantially lower refuse collection costs. However, there are various challenges associated with the use of automated refuse loaders. For example, it is desired that the refuse loader mechanism operate as fast as possible to reduce cycle times and increase productivity. However, when a refuse loader mechanism operates at high speed, large forces will be created if the mechanism suddenly comes to a stop or change direction. These forces can be very large, particularly when the loader mechanism is lifting a dumpster or other refuse container that can weigh in excess of several tons. These large forces can result in large stresses within mechanical components, leading to breakage, failure, or accelerated wear of components, or can result in pressure spikes in hydraulic components, also leading to breakage and failure of components.
One circumstance in which a refuse loader mechanism can suddenly come to a stop is when the mechanism reaches one of the ends of its range of travel. For example, in some refuse loader mechanisms, the range of travel is defined by stops or other components placed in the path of the mechanism to cause it to stop moving. These are often rigid components that cause the mechanism to stop rapidly upon striking the component. Some mechanisms are controlled by hydraulic actuators such as hydraulic cylinders, and where the range of travel is defined by the range of travel of the hydraulic cylinder. For example, when a piston inside of a hydraulic cylinder reaches either end of its stroke, the piston and its attached piston rod will rapidly come to a stop. In any case, rapidly stopping a refuse loader mechanism, and thereby also rapidly stopping whatever load the mechanism is carrying, can cause significant forces to be imparted to the mechanism and the rest of the machine. Other types of hydraulic actuators, such as rotary hydraulic actuators, also have a range of travel, and can also cause significant forces to be imparted to the mechanism and the rest of the machine if they are brought to a rapid stop. These loads can cause components to crack, welds to break, and bearings or bushings to wear out.
Another circumstance that can cause significant wear and tear on a refuse collection vehicle is when a lifting apparatus travels through a path that changes direction. For example, in some refuse collection vehicles, tracks for a lifting mechanism have a shape like a candy cane, with a tight turn at the top of the track. It is desired to reduce the shocks associated with the change in direction travel of the lifting apparatus.
There have been various systems proposed to reduce shocks associated with hydraulic cylinders approaching an end of their range of travel. One such system involves the use of hydraulic cushions within the hydraulic cylinder. These cushions generally function by creating a restricted flow path for hydraulic fluid to escape as the cylinder nears the end of its stroke, such that the trapped hydraulic fluid must be forced through a restriction and thereby slowing the motion of the cylinder. Furthermore, various mechanical devices have been adapted to the exterior of cylinders to dampen their motion near the end of their stroke, such as shock absorbers or mechanical kick-outs where a rod or linkage kicks out a hydraulic control valve as the cylinder approaches the end of its range of travel. However, the performance of these devices is often not optimum, because they may still allow a significant amount of shock in the system and are difficult to optimize for all conditions.
Other techniques have been used to control the speed of a hydraulic cylinder near the end of its stroke. One approach is the use of proportional electro-hydraulic control. This generally involves the use of one or more electrical solenoid valves to directly position a hydraulic control spool valve. An electrical signal can be sent to a solenoid valve to change the position of the hydraulic spool valve when the cylinder nears the end of its travel, causing the flow rate to the cylinder to be reduced and therefore causing the cylinder to slow before reaching its end of travel. However, systems of this construction tend to be expensive, because of the number of high precision components required. Moreover, these high precision components require close attention to maintenance practices and can more readily by damaged by contamination. Their intricate nature also renders them more difficult to service and repair, requiring greater levels of skill in maintenance personnel which can result in higher maintenance costs.
Improved systems for controlling motion of loader mechanisms on refuse collection vehicles are needed.